Disable GlowPad animation when alert activity is done

Bug: 9825266
The mPingEnabled was not set to flase when the alarm was dismissed, so the
handler was restarting the ping animation of the GlowPad.

Change-Id: I8e0de4ecd86a2a4df7237cd4cbe71aa97272a089
(cherry picked from commit b18aea794b2d81b15b78a338b6708231657518be)
Merge tag 'android-4.3_r3.1' of https://android.googlesource.com/platform/packages/apps/DeskClock into cm-10.2

Android 4.3 Release 3.1

Change-Id: I4bcb112bf5e12df67df2db3b8590c5f4a289da06